diff --git a/diff-sha.sh b/diff-sha.sh
index f4ca3cb5..d8ef6d6b 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -205,6 +205,10 @@ else
       fi
     else
       PREVIOUS_SHA=$GITHUB_EVENT_PULL_REQUEST_BASE_SHA
+      
+      if ! git diff --name-only --ignore-submodules=all "$PREVIOUS_SHA$DIFF$CURRENT_SHA" 1>/dev/null 2>&1; then
+        PREVIOUS_SHA=$(git merge-base "$PREVIOUS_SHA" "$CURRENT_SHA" 2>&1) && exit_status=$? || exit_status=$?
+      fi
     fi
 
     if [[ -z "$PREVIOUS_SHA" || "$PREVIOUS_SHA" == "$CURRENT_SHA" ]]; then
@@ -217,10 +221,10 @@ else
         max_depth=$INPUT_MAX_FETCH_DEPTH
 
         for ((i=0; i<max_depth; i+=depth)); do
-          echo "Fetching $depth commits..."
+          echo "Fetching $i commits..."
 
           # shellcheck disable=SC2086
-          git fetch $EXTRA_ARGS -u --progress --deepen="$depth" origin "$CURRENT_BRANCH"
+          git fetch $EXTRA_ARGS -u --progress --deepen="$i" origin "$CURRENT_BRANCH"
 
           if git diff --name-only --ignore-submodules=all "$PREVIOUS_SHA$DIFF$CURRENT_SHA" 1>/dev/null 2>&1; then
             break